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Old 01-13-2010, 04:51 PM
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How to tell if valve seals are bad

Hello all, here is what i have. 350 sbc crate motor, 5k miles(ish) 1405 edelbrock carb. performer intake, runs on 91 octane every fill-up. It recently started smoking from the left bank, but only at or above 2500 rpm (65-70 mph). It takes about 30-45 seconds of cruising at this speed and a bluish smoke (oil) starts to roll out, if I goose the throttle a huge puff comes out. and when I let off the throttle an almost dusty dark colored smoke rolls out. Im thinking the dusty colored smoke is fuel because I can hear the exhaust popping. I used new gaskets when I replaced the intake manifold, but is it possible, after a few hundred miles, they started leaking? I also thought i should look into the valve seals, but im not sure what the best way to check them is, should i pull the head? should I pull the valve? Im not sure what type they are, o ring or umbrella. If I pull the plugs and say, 3 is the only one that has black crusty deposits on it, would it be safe to say that is the valve or section of gasket causing the problem? any help is..well. helpful

Chris
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Old 01-13-2010, 05:26 PM
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Quote:
Originally Posted by Bonhorst
Hello all, here is what i have. 350 sbc crate motor, 5k miles(ish) 1405 edelbrock carb. performer intake, runs on 91 octane every fill-up. It recently started smoking from the left bank, but only at or above 2500 rpm (65-70 mph). It takes about 30-45 seconds of cruising at this speed and a bluish smoke (oil) starts to roll out, if I goose the throttle a huge puff comes out. and when I let off the throttle an almost dusty dark colored smoke rolls out. Im thinking the dusty colored smoke is fuel because I can hear the exhaust popping. I used new gaskets when I replaced the intake manifold, but is it possible, after a few hundred miles, they started leaking? I also thought i should look into the valve seals, but im not sure what the best way to check them is, should i pull the head? should I pull the valve? Im not sure what type they are, o ring or umbrella. If I pull the plugs and say, 3 is the only one that has black crusty deposits on it, would it be safe to say that is the valve or section of gasket causing the problem? any help is..well. helpful

Chris
I hate to say it but this sounds way more like either something bore or piston related or a cam lobe went bad.

Guide seals, or rather lack there-of, usually smoke on start up, idle, and deceleration. The reasons are:

1) Oil drips down the guides and puddles on the valves or past the open ones into the combustion chamber.

2) At idle the manifold vacuum is high and oil get pulled down the intake guides.

3) Similar to two, the vacuum is high and oil get sucked down the guide.

You could also be seeing:

1) The intake gaskets you used are open somewhere along the bottom of a port, or several, allowing oil to be pulled into the intake from the valley.

2) The ignition isn't getting across the plug that you pulled which is oily, but I must say this is a big indicator that a cam lobe or a lifter is gone, or perhaps a bent pushrod or some other cause that's keeping a valve on that cylinder from fully cycling. I'd make pulling a valve cover to watch the action high on my things to do list.

A compression test on the offending cylinder can lead to some info, as will putting in a fresh sparking bolt then shorting it to see if it's loss affects how the engine runs. A vacuum gauge is helpful, it shoud be steady, if it bounces around that could be a bad or not actuating valve, a steady low reading could be a gasket leak.

A leakdown test will find any bad rings or leaking valves as you can hear the air escaping where the problem is.

Bogie
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Old 01-13-2010, 06:35 PM
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Quote:
Originally Posted by oldbogie
I hate to say it but this sounds way more like either something bore or piston related or a cam lobe went bad.

Guide seals, or rather lack there-of, usually smoke on start up, idle, and deceleration. The reasons are:

1) Oil drips down the guides and puddles on the valves or past the open ones into the combustion chamber.

2) At idle the manifold vacuum is high and oil get pulled down the intake guides.

3) Similar to two, the vacuum is high and oil get sucked down the guide.

You could also be seeing:

1) The intake gaskets you used are open somewhere along the bottom of a port, or several, allowing oil to be pulled into the intake from the valley.

2) The ignition isn't getting across the plug that you pulled which is oily, but I must say this is a big indicator that a cam lobe or a lifter is gone, or perhaps a bent pushrod or some other cause that's keeping a valve on that cylinder from fully cycling. I'd make pulling a valve cover to watch the action high on my things to do list.

A compression test on the offending cylinder can lead to some info, as will putting in a fresh sparking bolt then shorting it to see if it's loss affects how the engine runs. A vacuum gauge is helpful, it shoud be steady, if it bounces around that could be a bad or not actuating valve, a steady low reading could be a gasket leak.

A leakdown test will find any bad rings or leaking valves as you can hear the air escaping where the problem is.

Bogie





I pulled the number 7 plug and you'll never guess what i found....you literally could not see any part of the plug past the threads due to the build up on the plug, here is a list of the plugs on a scale of 1 to 10, 10 being the worst 1 being that ever so smooth golden brown.
plug #1=1
plug#2=1
plug#3=4
plug#4=1
plug#5=5
plug#6=2
plug#7=10
plug#8=9
the first thing i tried after finding this, was to tighten the rear bolts on the intake but they were nice and tight. the second thing i tried was to re shoot the timing and take her for a spin, she ran real smooth no hesitation at idle on take off or at cruise. since it is dark out i cant tell if it is still smoking, but im sure as luck would have it..it is. Now i know cleaning the plug isnt going to solve my problem, so what do you think could have caused it? the build up was hard crispy and black, and smelled like burnt oil (go figure). i would just like to know how it got there. I would have never thought about the lobes, and now that you mention it when i replaced my valve cover gaskets yesterday, I think one of the push rods for 7 looked a litte funny, cause I remember very well doing a double take at it and then deciding it looked fine, but i think it deserves another look see. and since there is that much build up on the plug, then it may be building up on the valve too and keeping it open just a smidge? but then why would it be running so smooth? before i cleaned the plug it was just a tad hesitant no matter what. let me know what you think, and please keep in mind the condition of all the plugs on the left bank. my gut is telling me to go after the intake gaskets

Chris
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Old 01-13-2010, 07:16 PM
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valve seals would be at high vacuum and when fired up for a few seconds and then would clear right up. high miuleage engines do this because the seals turn brittle and bust apart. new engines may smoke until broken in due to rings not seated yet and id be looking at that in this case.

wrong size rings or not broken in, or improperly prepared walls.
or improperly phased/installed rings

but coul dbe something else, head gaskets allowing oil to get sucked in,

evne possibly intake gaskets, bad angle between heads and intake, especially if the heads are milled
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Old 01-13-2010, 07:22 PM
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'oldbogey' is right on. Put a vacuum gauge on it like he suggested it will tell you VOLUMES about what is going on inside your engine. If you have no other diagnostic tool in your tool box you should have a vacuum gauge. I mount one permanently in all my older vehicles. It can alert you to a problem before you would notice it otherwise.
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